I. Field of the Invention
The present invention relates generally to crankshafts and, more particularly, to a method and apparatus for constructing a multi-piece crankshaft.
II. Description of the Prior Art
In a conventional crankshaft, the crankshaft includes a segmented main shaft having an axis aligned with the axis of rotation of the crankshaft. One or more crankpins are also provided at a position radially spaced from, but parallel to, the main shaft. The piston is then secured to each crankpin which rotatably drives the crankshaft about its axis of rotation.
Since the crankpins are radially offset from the axis of rotation of the crankshaft and attached to a piston, counterweights are conventionally provided for securing the main shaft to the crankpins so that the overall crankshaft has a balanced rotation. In many previously known crankshafts, the entire crankshaft is made from a single heavy body of cast metal which is then machined so that the main shaft, crankpins and counterweights are of a one piece construction. Machining such crankshafts, however, is necessarily expensive which increases the overall cost of the crankshaft.
There have, however, been crankshafts which are constructed from multiple pieces for low cost construction. Such crankshafts are oftentimes used in small two cycle engines although they can be used in other types of engines or compressors.
Typically, the counterweights are constructed from an inexpensive material, such as powdered metal or steel stampings, and the counterweight has holes formed through it corresponding to the position of the crankpin and main shaft. The crankpin and main shaft are then constructed from conventional round stock. The ends of the main shaft and crankpins are knurled, splined or otherwise deformed and pressed into the openings formed in the counterweight to thereby form the crankshaft.
One primary disadvantage of these previously known multi-piece crankshafts is that the main shaft and crankpins must be parallel to each other within very high tolerances. However, during the pressing operation, the main shaft and crankpins often become skewed relative to each other and the resulting crankshaft assembly must be either corrected by bending the crankpin and main shaft relative to each other or, in some cases discarded as scrap. Furthermore, these prior art crankshafts were also subject to failure from push out and twisting of the shaft relative to the counterweight.